With the participation of international ensembles/performers, theMusica Aeterna Art Foundationisplanning to reconstruct the 500-year-old liturgical music of the Habsburg imperial court. The repertoire embraces the music for Sundays and church festivals for the entire liturgical year, which means 238 concerts. Due to the large number of concerts we plan to accomplish this within three seasons. The project is foreseen to begin on 30 November 2008 (first Sunday of Advent) and end on 22 November 2011 (festival of Saint Cecilia, patron saint of music). The complete vocal repertoire would draw on two major contemporary sources, which were published 500 years ago—which is symbolically represented in the starting and ending date of the project.The Gregorian movements of the liturgy are taken from the Graduale Pataviense. This codex contains the liturgical music of the Passau archbishopric, according to which the services in the imperial court were held. This volume forms the basis of Heinrich Isaac’s Choralis Constantinus whose volumes contain the polyphonic music for the entire liturgical year. The composer was commissioned by the Bishop of Konstanz to compose this collection—unique in music and cultural history—in 1508, who devoted the end of his career to it. The Flemish-born Isaac first appeared in the service for the Medici family in Florence, later he worked for the Emperor Maximilian, becoming imperial Kapellmeister. He composed the music for the Choralis Cosntantinus according to the practices of the imperial court. The job was finished by his young and gifted pupil Ludwig Senfl, who succeeded him in his post. In the last years of his life Isaac left the court and returned to Florence to manage the affairs of the Medici family. Pope Leo X, a former pupil of Isaac’s, had asked his trusty old tutor to do so.After the emperor’s death in 1519 the Kapella was disbanded and Senfly had to leave. In 1523 he was in thee court of the Bavarian duke, where he completed the collection his master had started. After long adventures, the manuscript finally appeared in print in 1550 and 1555. The three-volume polyphonic collection is extremely significant. It crowns the church music tradition ranging from the emergence of polyphony to the Renaissance. Musically, it is a kind of summary which bears every feature of the development of Flemish compositional technique. It is a forerunner of later complete editions (opera omnia). Neither beforehand, nor later in history was there published a work of such significance, comprising the music for the entire liturgical year. Some composers made attempts at this (such as Byrd and Palestrina), but their efforts were either incomplete or remained in the planning stage.The Choralis Constantinus had been copied and distributed as a manuscript, but now that it was published, it spread quickly throughout Europe. Its survival was thwarted by the spread of Protestantism and the reforms of the Council of Trent with its introduction of a centralised liturgical practice.This project is extremely important in that it evokes and presents to the modern European audiences a unique, 500-year-old cultural/musical treasure in international cooperation, perhaps for the first time in history at one location, in complete form.